Variable phase shifting circuit manufactured in simple integrated circuit

ABSTRACT

A variable phase shifting circuit includes a resistance unit and a variable capacitance unit. The resistance unit includes at least one resistor element. The resistance unit input a first signal and a second signal and also output a third signal and a fourth signal. The variable capacitance unit includes two base-to-emitter capacitors of two transistors. The variable capacitance unit is connected to the third signal and the fourth signal. The two base-to-emitter capacitors is varied by controlling collector currents of the two transistors. The third signal and the fourth signal are produced by shifting phases of the first and second signals based on the at least one resistor element and the two base-to-emitter capacitors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a variable phase shiftingcircuit and a variable phase shifting method. More specifically, thepresent invention is directed to such a variable phase shifting method,and also a variable phase shifting circuit easily manufactured in anintegrated circuit with a simple circuit arrangement.

2. Description of the Related Art

Conventionally, RC variable phase shifting circuits play an importantrole specifically in signal processing systems operable in microwavefrequency ranges. The RC variable phase shifting circuits are generallycomposed of resistor elements and capacitor elements, and any one ofresistor element and capacitor element is constructed as a variableelement.

Japanese Laid Open Patent Application (JP-A-Heisei 1-268217) describesthe variable phase shifting circuit capable of realizing the broadbandvariable width. In this variable phase shifting circuit, the emitter ofthe first transistor is connected via the first resistor element to thefirst power supply terminal, and the collector of this transistor isconnected via the second resistor element to the second power supplyterminal.

The series circuit is connected between the collector of the firsttransistor and the emitter thereof. This series circuit is composed ofthe second transistor and the third resistor element. The base of thissecond transistor is connected to the emitter thereof as the variablecapacitor element. Otherwise, the base of the second transistor isconnected to the collector thereof.

In this variable phase shifting circuit, the emitter of the thirdtransistor is connected via the fourth resistor element to the firstpower supply terminal, and the collector of this third transistor isconnected via the fifth resistor element to the second power supplyterminal.

The series circuit is connected between the collector of the thirdtransistor and the emitter thereof. This series circuit is composed ofthe fourth transistor and the sixth resistor element. The base of thissecond transistor is connected to the emitter thereof as the variablecapacitor element. Otherwise, the base of the third transistor isconnected to the collector thereof.

Furthermore, in this variable phase shifting circuit, both the base ofthe first transistor and the base of the third transistor are connectedto the input terminal. The junction point between the second transistorand the third resistor element is connected to the first outputterminal. Also, the junction point between the fourth transistor and thesixth resistor element is connected to the second output terminal.

Either the emitter of the first transistor or the collector thereof isconnected to the collector of the second transistor, and either theemitter of the third transistor or the collector thereof is connected tothe fourth transistor. It should be noted that in this variable phaseshifting circuit, a field-effect transistor (FET) may be employed aseach of the above-explained transistors.

On the other hand, Japanese Laid Open Utility Application (JP-U-Heisei2-126431) discloses a monolithic variable phase shifting circuit. Inthis reference, an input signal is supplied to a first phase shiftingcircuit and a second phase shifting circuit such that the input signalis separated into two signals having the phase difference of 90 degrees.

Also, in this monolithic variable phase shifting circuit, the firstinput signal is supplied to the first phase shifting circuit while thesecond input signal is supplied to the second phase shifting circuit,such that these input signals are synthesized into a signal not to havea phase difference.

In each of the first phase shifting circuit and the second phaseshifting circuit, both of the collector of the transistor and theemitter thereof are grounded in order that the DC voltage can be appliedvia the resistor element. Also, the series circuit is connected betweenthe collector of the transistor and the emitter thereof. This seriescircuit is composed of the variable capacitor element, the fixedcapacitor element, and the resistor element. This variable capacitorelement is formed by the junction capacitance of the transistor.

The base of the transistor is connected to the input terminal. Eitherthe junction point between the variable capacitor element and theresistor element or another junction between the fixed capacitor elementand the resistor element is connected to the output terminal.

Furthermore, since the variable capacitance element is connected Inparallel to the fixed capacitor element, the degradation of thefrequency characteristic can be suppressed. It should also be noted thatfield-effect transistors may be employed as the respective transistorsin this monolithic phase shifting circuit.

Further, Japanese Laid Open Patent Application (JP-A-Heisei 3-26015)discloses the voltage variable phase shifter for controlling the phaseof the signal by controlling the voltage by the transistor circuit.

In this voltage-controlled variable phase shifter, the collector of thefirst transistor is grounded so as to vary the phase of the inputsignal. The second transistor controls the emitter current supplied fromthe first transistor in response to the controlling variable voltage.Also, the fixed capacitor element is connected between the emitter ofthe first transistor and the ground.

In response to the change in the controlling variable voltage, thisvoltage-controlled variable phase shifter changes the output impedanceof the first transistor. Furthermore, both this changed output impedanceand the fixed capacitance element determines the phase shift amount.

FIG. 1A and FIG. 1B represent RC variable phase shifting circuits knownin this technical field. The RC variable phase shifting circuit shown inFIG. 1A is composed of the resistor element R and the variable capacitorelement C′. The predetermined phase shifting amount with respect to theinput signal may be obtained by adjusting the capacitor value of thevariable capacitor element C′.

Also, the RC variable phase shifting circuit shown in FIG. 1B iscomposed of the capacitor element C and the variable resistor elementR′. The desirable phase shifting amount with respect to the input signalmay be obtained by adjusting the resistor value of the variable resistorelement R′.

In the case that the above-explained RC variable phase shifting circuitsshown in FIG. 1A and FIG. 1B are realized as the integrated circuit, thefollowing problem will arise. That is, it is practically difficult toassemble the variable resistor element R′ into the semiconductor elementas to the known RC variable phase shifting circuit shown in FIG. 1B.

Also, in the RC variable phase shifting circuit represented in FIG. 1A,for example, the variable capacitor realized by utilizing the reversebiasing of the transistor, which may function as the variable capacitorelement C′, has been proposed.

However, when the variable capacitor element by using the reversebiasing of the transistor is assembled into the semiconductor element,if the junction capacitor between the base and the emitter is utilized,then the voltage withstanding level is low.

Under such a circumstance, this reverse biasing variable capacitorelement can be hardly applied to the semiconductor element. Also, whenthe junction capacitor established between the base-to-emitter path isused, the change amount of the phase shift is very small. As aconsequence, it is practically difficult to obtain a desirable phaseshift amount.

SUMMARY OF THE INVENTION

The present invention is accomplished to solve the above-mentionedproblems. Therefore, an object of the present invention is to provide avariable phase shifting circuit and a variable phase shifting method,which is easily manufactured in an integrated circuit with a simplecircuit arrangement.

In order to achieve an aspect of the proposed invention, a variablephase shifting circuit may include a resistance unit and a variablecapacitance unit.

The resistance unit may include at least one resistor element, forinputting a first signal and a second signal and also for outputting athird signal and a fourth signal. The variable capacitor unit mayinclude two base-to-emitter capacitances of two transistors. Thevariable capacitor unit may be connected to the third signal and thefourth signal.

In this case, the two base-to-emitter capacitances may be varied bycontrolling collector currents of the two transistors. Also, the thirdsignal and the fourth signal may be produced by shifting phases of thefirst and second signals based on the at least one resistor element andthe two base-to-emitter capacitances.

The resistance unit may include a first resistor element connected tothe first signal, for outputting the third signal, and a second resistorelement connected to the second signal, for outputting the fourthsignal. Also, the second signal is supplied to have a potential of theground level.

Instead, the resistance unit may include a first resistor elementconnected to the first signal, for outputting the third signal. Thesecond signal may be outputted as the fourth signal. In this case, thesecond signal is supplied to have a variable DC potential Vbias2.

The variable capacitance unit may include an amplifying unit having afirst transistor and a second transistor, and a constant current source.In the amplifying unit, a collector of the first transistor and acollector of the second transistor are connected to a potential Vcc.Also, a base of the first transistor is connected to the third signal.In addition, a base of the second transistor is connected to the fourthsignal.

The constant current source is connected between the emitters of thefirst and second transistors, and the potential of the ground level. Theconstant current source controls the collector currents of the first andsecond transistors. Also, the constant current source may be a variabletype constant current source.

The variable phase shifting circuit may further include a differentialamplifier unit for eliminating in-phase signal components contained inthe third signal and the fourth signal. The second amplifier unit mayinclude a third transistor and a fourth transistor and a fifthtransistor.

In the differential amplifier unit, a collector of the third transistoris connected via a third resistor element to the potential of Vcc. Acollector of the fourth transistor is connected via a fourth resistorelement to the potential of Vcc. A base of the third transistor isconnected to the third signal. A base of the fourth transistor isconnected to the fourth signal.

Also, a base of the fifth transistor is connected to a DC potentialVbias1. A collector of the third transistor is connected to an emitterof the third transistor and an emitter of the fourth transistor. Anemitter of the fifth transistor is connected via a fifth resistorelement to the potential of the ground level.

The variable capacitance unit may include the amplifying unit having afirst transistor and a second transistor, and a constant current source.In the amplifying unit, a collector of the first transistor and acollector of the second transistor are connected to the potential Vcc. Abase of the first transistor is connected to the third signal. A base ofthe second transistor is connected to the fourth signal.

The constant current source is connected between emitters of the firstand second transistors, and the potential of the ground level. Theconstant current source controls the collector currents of the first andsecond transistors based on the second signal having a potential ofvariable DC potential Vbias2. In this case, the constant current sourcemay be a fixed type constant current source.

A phase variable shifting method may include the steps of supplying stepand shifting step. In the supplying step, a first signal and a secondsignal may be supplied. Next, in the shifting step, a phase of the firstsignal and a phase of the second signal may be shifted based on changeof base-to-emitter capacitances of a first transistor and secondtransistor.

In this case, the shifting step may include steps of a deciding step anda controlling step and a changing step. In the deciding step, collectorcurrent values of the first and second transistors may be decided basedon a predetermined phase-shift value. Next, in the controlling step, thecollector current of the first and second transistors may be controlledbased on the decided collector current values. Next, in the changingstep, the base-to-emitter capacitances of the first and secondtransistors may be changed.

In addition, the step of shifting a phase of the first signal isexecuted in synchronism with the step of shifting a phase of the secondsignal.

The phase variable shifting method may further include eliminating step.In the eliminating step, in-phase signal components contained in thephase-shifted first signal and the phase-shifted second signal may beeliminated.

A variable phase shifting circuit may include a first resistor elementand a second resistor element and an amplifying unit having a firsttransistor and a second transistor, and a constant current source ofvariable type.

The first resistor element is connected to a first signal, foroutputting a second signal. The second resistor element is connected toa third signal, for outputting a fourth signal.

A collector of the first transistor and a collector of the secondtransistor are connected to a potential Vcc. A base of the firsttransistor is connected to the second signal. A base of the secondtransistor is connected to the fourth signal. The constant currentsource is connected between an emitter of the first transistor, anemitter of the second transistor, and a potential of the ground level.

Also, a variable phase shifting circuit may include a first resistorelement and a second resistor element and an amplifying unit having afirst transistor and a second transistor, and a constant current sourceof variable type, and a differential amplifier unit having a thirdtransistor and a fourth transistor and a fifth transistor.

The first resistor element is connected to a first signal, foroutputting a second signal. The second resistor element is connected toa third signal, for outputting a fourth signal.

A collector of the first transistor and a collector of the secondtransistor are connected to a potential Vcc. A base of the firsttransistor is connected to the second signal. A base of the secondtransistor is connected to the fourth signal. The constant currentsource is connected between an emitter of the first transistor, anemitter of the second transistor, and a potential of the ground level.

A collector of the third transistor is connected via a third resistorelement to the potential Vcc. A collector of the fourth transistor isconnected via a fourth resistor element to the potential Vcc. A base ofthe third transistor is connected to the second signal. A base of thefourth transistor is connected to the fourth signal.

A base of the fifth transistor is connected to a DC potential Vbias1. Acollector of the fifth transistor is connected to an emitter of thethird transistor and an emitter of the fourth transistor. An emitter ofthe fifth transistor is connected via a fifth resistor element to thepotential of the ground level.

In addition, a variable phase shifting circuit may include a firstresistor element and a second resistor element, and an amplifying unithaving a first transistor and a second transistor, and a constantcurrent source of variable type.

The first resistor element is connected to a first signal, foroutputting a second signal. The second resistor element is connected toa third signal supplied to have a potential of the ground level, foroutputting a fourth signal.

A collector of the first transistor and a collector of the secondtransistor are connected to a potential Vcc. A base of the firsttransistor is connected to the second signal. A base of the secondtransistor is connected to the fourth signal. The constant currentsource is connected between an emitter of the first transistor, anemitter of the second transistor, and the potential of the ground level.

Instead, a variable phase shifting circuit may include a first resistorelement and an amplifying unit having a first transistor and a secondtransistor, and a constant current source of fixed type.

The first resistor element is connected to a first signal, foroutputting a second signal. A third signal supplied to have a variableDC potential is outputted as a fourth signal.

A collector of the first transistor and a collector of the secondtransistor are connected to a potential Vcc. A base of the firsttransistor is connected to the second signal. A base of the secondtransistor is connected to the fourth signal.

The constant current source is connected between an emitter of the firsttransistor, an emitter of the second transistor, and a potential of theground level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically indicates the conventional RC variable phaseshifting circuit;

FIG. 1B schematically represents another conventional RC variable phaseshifting circuit;

FIG. 2 is a schematic block diagram for showing a technical concept of avariable phase shifting circuit accomplished in accordance with thepresent invention;

FIG. 3 is a circuit diagram for representing a variable phase shiftingcircuit according to a first embodiment of the present invention;

FIG. 4 graphically represents a relationship between a base-to-emittercapacitance and a collector current of a transistor employed in thevariable phase shifting circuit of FIG. 3;

FIG. 5 graphically represents a phase shift amount in a frequency rangeof the variable phase shifting circuit shown in FIG. 3, while using acurrent value as a parameter, controlled by a constant current sourceindicated in FIG. 3;

FIGS. 6A to 6D are timing charts for describing operations of thevariable phase shifting circuit shown in FIG. 3, namely, FIG. 6Aindicates a waveform of a first signal; FIG. 6B indicates a waveform ofa second signal; FIG. 6C indicates a waveform of a third signal; andFIG. 6D indicates a waveform of a fourth signal;

FIG. 7 is a circuit diagram for showing a variable phase shiftingcircuit according to a second embodiment of the present invention;

FIG. 8 is a schematic block diagram for indicating a transmission systemto which the second variable phase shifting circuit of FIG. 7 isapplied;

FIG. 9 is a circuit arrangement for representing a variable phaseshifting circuit according to a third embodiment of the presentinvention; and

FIG. 10 is a circuit arrangement for indicating a variable phaseshifting circuit according to a fourth embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, a variable phase shifting circuit of the present invention will bedescribed below in detail with reference to the attached drawings.

FIG. 2 is a schematic block diagram for explaining a basic idea(conceptual idea) of a variable phase shifting circuit according to thepresent invention. This basic variable phase shifting circuit includes aresistance unit 101 and a variable capacitance unit 103.

The resistance unit 101 includes at least one resistor element (notshown in detail). A first signal 105 supplied from an input terminal IN1and a second signal 107 supplied from another input terminal IN2 areinputted into the resistance unit 101. Then, a third signal 109 and afourth signal 111 are outputted from the resistance unit 101. The thirdsignal 109 and the fourth signal 111 are derived from an output terminalOUT1 and another output terminal OUT2.

The variable capacitance unit 103 includes two base-to-emittercapacitances (not shown either) in two sets of transistors. Thisvariable capacitance unit 103 is connected to the third signal 109 andthe fourth signal 111 outputted from the resistance unit 101.

Also, these two base-emitter capacitances included in this variablecapacitance unit 103 are operable as a variable capacitor element. Thisimplies that collector currents of these two transistors are controlled.

In addition, both of the third signal 109 and the fourth signal 111 maybe produced by shifting phases of the first signal 105 and the secondsignal 107, based on at least one of resistor elements of the resistanceunit 101 and the two base-emitter capacitances of the variablecapacitance unit 103.

This implies that the first signal 105 is phase-shifted on change ofone, corresponding to the first signal 105, of the base-emittercapacitances of the two transistors. On the other hand, the secondsignal 107 is phase-shifted on change of the other, corresponding to thesecond signal 107, of the base-emitter capacitances of the twotransistors.

It should be understood that the variable phase shifting circuitindicated in FIG. 2 corresponds to a 2-input/2-output system.Alternatively, this basic variable phase shifting circuit may be appliedas a 1-input/1-output system. This 1-input/1-output system may berealized by such that any one of the first signal 105 and the secondsignal 107, corresponding to the input signal, is supplied to have apredetermined potential (will be discussed later).

FIG. 3 represents a circuit arrangement of a variable phase shiftingcircuit according to a first preferred embodiment of the presentinvention. This variable phase shifting circuit of this first embodimentincludes a resistance unit 101-1 and a variable capacitance unit 103-1.

The resistance unit 101-1 includes a first resistor element R1 and asecond resistor element R2. The first resistor element R1 is connectedto the first signal 105 supplied from the input terminal IN1. The firstresistor element R1 outputs the third signal 109 outputted from theoutput terminal OUT1. The second resistor element R2 is connected to thesecond signal 107 supplied from the another input terminal IN2. Thesecond resistor element R2 outputs the fourth signal 111 outputted fromanother output terminal OUT2.

The variable capacitance unit 103-1 includes an amplifier unit 113 and aconstant current source Iv. Furthermore, the amplifier unit 113 includesa first transistor Q1 and a second transistor Q2. A collector of thefirst transistor Q1 and a collector of the second transistor Q2 areconnected to a first potential Vcc.

Also, a base of the first transistor Q1 is connected to the third signal109, and a base of the second transistor Q2 is connected to the fourthsignal 111. In this first embodiment, the first potential Vcc is set toa voltage range of 1[V] to 5[V].

The constant current source Iv of a variable type is connected betweenthe emitters of the first and second transistors (Q1 and Q2), and asecond potential equal to the ground level. In other words, emittercurrents of these two transistors (Q1 and Q2) are inputted to thisconstant current source Iv.

Furthermore, this constant current source Iv adjusts the inputtedcurrent to values corresponding to a predetermined phase-shift amount.Therefore, collector currents of the first and second transistors (Q1and Q2) can be controlled so as to vary a base-to-emitter capacitance ofeach of the two transistors (Q1 and Q2).

The first signal 105 inputted from the input terminal IN1 and the secondsignal 107 inputted from the input terminal IN2 are same butcomplementary in phase. Also, the first transistor Q1 and the secondtransistor Q2 are such electronics elements having the samecharacteristics. As a consequence, a current of the first transistor Q1and a current of the second transistor Q2 are same but complementary inphase.

The base-to-emitter capacitance Cπ of each of the first and secondtransistors (Q1 and Q2) is expressed as follows:

Cπ=Cb+Cje   (1),

where symbol “Cb” indicates a base capacitance, and symbol “Cje”indicates an emitter-to-base junction capacitance.

Furthermore, this base capacitance Cb is expressed as follows:

Cb=τ _(F) g _(m)=τ_(F)(q·I _(c) /k T)   (2),

where symbol “τ_(F)” indicates base propagation time, symbol “g_(m)”indicates mutual inductance, q/k T=26 [mV], and symbol “I_(c)” indicatesa collector current. The above defined two formulae may indicate thatthe base-to-emitter capacitance “Cπ” is a function of the collectorcurrent “Ic”.

FIG. 4 graphically represents a change in the base-to-emittercapacitance Cπ in the case that the current flowing through the constantcurrent source Iv shown in FIG. 3 is varied. That is, FIG. 4 indicatessuch a fact that since the current flowing through the constant currentsource Iv is varied within a range between 1 [mA] to 8 [mA], thebase-to-emitter capacitance “Cπ” is varied within a range between 100[fF] and 1200 [fF].

In accordance with this first embodiment, the constant current Iv isadjusted so as to control the collector currents Ic of the first andsecond transistors (Q1 and Q2). Therefore both the phase of the thirdsignal 109 and the phase of the fourth signal 111, which correspond tothe output signals of this variable phase shifting circuit, may beshifted by about 0 to 20 degrees.

FIG. 5 graphically represents a phase change in a frequency region,while the current flowing through the constant current source Iv is usedas a parameter within a current range between 1 [mA] and 4 [mA].

Referring now to the circuit arrangement of FIG. 3 and a timing chartshown in FIG. 6, a phase variable shifting operation of theabove-explained variable phase shifting circuit according to the firstembodiment of the present invention will be described.

First, both the first signal 105 and the second signal 107 are suppliedas input signals to this variable phase shifting circuit. These firstand second signals are complementary in phase (see FIG. 6A and FIG. 6B).Next, a phase of the first signal 105 and a phase of the second signal107 are shifted based on change of base-to-emitter capacitances of afirst transistor Q1 and second transistor Q2.

In detail, a phase of the first signal 105 and a phase of the secondsignal 107 are shifted by the following process. First, collectorcurrent values of the first and second transistors (Q1 and Q2) aredecided based on a predetermined phase-shift value. Next, the collectorcurrents of the first and second transistors (Q1 and Q2) are controlledbased on the decided collector current values, respectively. Next, thebase-to-emitter capacitances of the first and second transistors arechanged.

In the above-described first embodiment, the current value of thevariable type constant current source Iv can be adjusted. Therefore,both the collector current of the first transistor Q1 and the collectorcurrent of the second transistor Q2 are controlled, so that thebase-to-emitter capacitances of these two transistors can be varied.

In accordance with the above-explained operation, the third signal 109may be produced by phase-shifting the fist signal 105 by thepredetermined phase shift amount (see FIG. 6C). Similarly, the fourthsignal 111 may be produced by phase-shifting the second signal 107 bythe predetermined phase shift amount (see FIG. 6D).

As apparent from the waveform charts shown in FIG. 6C and FIG. 6D, thesame phase shift amounts are given to the third signal 109 and thefourth signal 111. Further, the process of shifting the first signal 105is executed in synchronism with the process of shifting the secondsignal 107 (time T2→time T2′).

This synchronized operation can be performed by controlling thecollector currents of the first and second transistors (Q1 and Q2) atthe same time. The collector currents of the first and second transistor(Q1, and Q2) are produced from the first signal 105 and the secondsignal 107 having the phase-complementary relationship with the firstsignal.

It should be understood that when the first potential Vcc is set toapproximately 3[V], the voltage levels of the first signal 105 and thesecond signal 107 are set within a voltage range between approximately0.2[V] and 2[V]. This voltage level may be applied to other preferredembodiments.

FIG. 7 shows a circuit diagram of a variable phase shifting circuitaccording to a second embodiment of the present invention. This variablephase shifting circuit includes a resistance unit 101-1, a variablecapacitance unit 103-1 and a second differential amplifier unit 115. Itshould be understood that the arrangements and the operations of theresistance unit 101-1 and the variable capacitance unit 103-1 areidentical to those of the first embodiment shown in FIG. 3.

The variable phase shifting circuit of the second embodiment involves adifferent circuit arrangement, namely the employment of the differentialamplifier unit 115. The function of this differential amplifier unit 115is to eliminate an in-phase component contained in a third signal 109and a fourth signal 111.

The third signal 109 is produced by phase-shifting the first signal 105on a predetermined phase shift amount, while the fourth signal 111 isproduced by phase-shifting the second signal 107 on a predeterminedphase shift amount. The variable phase shifting circuit 117 of thissecond embodiment further including this differential amplifier unit 115may be extended as a transmission system with high performance.

The differential amplifier unit 115 includes a third transistor Q3, afourth transistor Q4 and a fifth transistor Q5. A collector of thisfourth transistor Q4 is connected via a fourth resistor element R4 tothe first potential Vcc, and a collector of the fifth transistor Q5 issimilarly connected via a fifth resistor element R5 to the firstpotential Vcc. A base of the fourth transistor Q4 is connected to thethird signal 109, and a base of the fifth transistor Q5 is connected tothe fourth signal 111.

Also, a base of the third transistor Q3 is connected to a thirdpotential having a DC potential Vbias1. A collector of the thirdtransistor Q3 is connected to an emitter of the fourth transistor Q4 andan emitter of the fifth transistor Q5. An emitter of the thirdtransistor Q3 is connected via a third resistor element R3 to a secondpotential equal to the ground level.

In variable phase shifting circuit of this second embodiment, the firstpotential Vcc is set to a voltage range between 3[V] and 5[V]. The thirdpotential equal to the DC potential Vbias1 is set to another voltagerange between 0.3[V] and 1.5[V].

FIG. 8 schematically shows a transmission system to which the variablephase shifting circuit according to the second embodiment has beenapplied. This transmission system includes a variable phase shiftingcircuit (117, and 117′), a quadrature phase shifting modulator (119, and119′), and a synthesizing amplifier 121.

Two sets of the above-described variable phase shifting circuits (117,and 117′) are prepared as the systems having the essentially samecharacteristics, and two sets of the above-described quadrature phaseshifting modulators (119, and 119′) are prepared as the systems havingthe essentially same performance.

One variable phase shifting circuit 117 phase-shifts the first inputsignal 123 inputted from the input terminal IN11, and also the secondinput signal 125 inputted from the input terminal IN12 on predeterminedphase shift amounts. Also, on the other hand, the other variable phaseshifting circuit 117′ phase-shifts the third input signal 127 inputtedfrom the input terminal IN21, and also the fourth input signal 129entered from the input terminal IN22 on the predetermined phase shiftamounts.

As to the phase shift aspect, both the first input signal 123 and thesecond input signal 125 are the same signals but complementary in phase.Also, both the third input signal 127 and the fourth input signal 129are the same signals but complementary in phase. The first input signal123 and the third input signal 127 are the same signals having a phasedifference of 90 degrees from each other.

Both a phase-shifted first input signal and the phase-shifted secondinput signal are supplied to one quadrature phase shifting modulator 119so as to be quadrature-phase-modulated. Also, both the phase-shiftedthird input signal and the phase-shifted fourth input signal aresupplied to the other quadrature phase shifting modulator 119′ in orderto be quadrature-phase-modulated.

As a result, two sets of the quadrature phase shifting modulators 119and 119′ output signals having phase difference of 0, 90, 180, and 270degrees. These phase difference signals are synthesized with each otherby the synthesizing amplifier 121 to thereby output a synthesizedsignal.

In the case that a phase difference between the first input signal 123and the third input signal 127 is equal to 90 degrees+α and 90degrees−α, this phase difference of +α and −α can be adjusted bycontrolling the current of the constant current source employed in anyone of these variable phase shifting circuits (117, and 117′).

FIG. 9 shows a circuit diagram of a variable phase shifting circuitaccording to a third embodiment of the present invention. This variablephase shifting circuit includes a resistance unit 101-1 and a variablecapacitance unit 103-1. It should be understood that the arrangementsand the operations of the resistance unit 101-1 and the variablecapacitance unit 103-1 are identical to those of the first embodimentshown in FIG. 3.

The variable phase shifting circuit of the third embodiment involves adifferent circuit arrangement, namely a second signal 107 is supplied tohave a potential equal to the ground level, as compared with the firstembodiment. Furthermore, since a fourth signal 111 produced byphase-shifting the second signal 107 is not outputted from the outputterminal, this variable phase shifting circuit corresponds to a1-input/1-output system.

A phase variably shifting operation of the above-explained variablephase shifting circuit according to the third embodiment of the presentinvention will be described.

First, both a first signal 105 and the second signal 107 are supplied asinput signals to this variable phase shifting circuit. The second signal105 is substantially zero. Next, a phase of the first signal 105 isshifted based on change of a base-to-emitter capacitance of a firsttransistor Q1.

In detail, a phase of the first signal 105 is shifted by the followingprocess. First, a collector current value of the first transistor Q1 isdecided based on a predetermined phase-shift value. Next, the collectorcurrent of the first transistor Q1 is controlled based on the decidedcollector current value. Next, the base-to-emitter capacitance of thefirst transistor Q1 is changed.

Similar to the first embodiment, in accordance with this thirdembodiment, since the emitter current of the first transistor Q1 iscontrolled by the variable type constant current source Iv, thecollector current of the first transistor Q1 is controlled. The firstpotential Vcc is set to a voltage range between 1[V] and 5[V].

FIG. 10 is a circuit arrangement of a variable phase shifting circuitaccording to a fourth embodiment of the present invention. The fourthvariable phase shifting circuit includes a resistance unit 101-2 and avariable capacitance unit 103-2.

This variable phase shifting circuit of the fourth embodiment involves adifferent circuit arrangement from that of the first embodiment. Thatis, the second signal 107 is supplied to have a potential equal to thevariable DC potential Vbias2. Moreover, the variable phase shiftingcircuit according to the fourth embodiment corresponds to a1-input/1-output system.

The resistance unit 101-2 includes a first resistor element R1. Thefirst resistor element R1 is connected to the first signal 105, foroutputting a third signal 109. Also, a second signal 107 is outputted asthe fourth signal 111. The second signal 107 is supplied to have afourth potential equal to a variable DC potential Vbias2.

The variable capacitance unit 103-2 includes an amplifying unit 113 anda constant current source It. Furthermore, the amplifying unit 113includes a first transistor Q1 and a second transistor Q2.

Both a collector of the first transistor Q1 and a collector of thesecond transistor Q2 are connected to the first potential Vcc. A base ofthis first transistor Q1 is connected to the third signal 109. A base ofthe second transistor Q2 is connected to the fourth signal 111.

The constant current source It is a fixed type constant current sourceconnected between the emitters of the first and second transistors (Q1and Q2), and a second potential equal to the ground level. This constantcurrent source “It” controls the collector currents of the first andsecond transistors (Q1 and Q2) based on the controlled potential of theDC potential Vbias2.

The phase variably shifting operation of the above-explained variablephase shifting circuit according to the fourth embodiment of the presentinvention will be described.

First, both the first signal 105 and the second signal 107 are suppliedas input signals to this variable phase shifting circuit. The secondsignal 105 is supplied on the DC potential Vbias2. Next, a phase of thefirst signal 105 is shifted based on change of base-to-emittercapacitances of the first transistor Q1 and second transistor Q2.

In detail, a phase of the first signal 105 is shifted as followingprocess. First, a collector current value of the first transistor Q1 isdecided based on a predetermined phase-shift value. Next, the collectorcurrent of the first transistor Q1 is controlled based on the decidedcollector current value and the DC potential Vbias2. Next, thebase-to-emitter capacitance of the first transistor Q1 is changed.

In accordance with this fourth embodiment, since the emitter current ofthe first transistor Q1 is controlled by the fixed type constant currentsource It, the collector current of the first transistor Q1 iscontrolled. The first potential Vcc is set to a voltage range between1[V] and 5[V]. Also, the variable DC potential Vbias2 is set to avoltage range between 1.5[V] and 2.5[V].

What is claimed is:
 1. A variable phase shifting circuit comprising: aresistance unit including at least one resistor element, for inputting afirst signal and a second signal and also for outputting a third signaland a fourth signal; and a variable capacitance unit comprising a firsttransistor, a second transistor operatively coupled to said firsttransistor and a constant current source for sinking a current fromemitters of said first and second transistors, wherein the base of saidfirst transistor is coupled to said third signal and the base of saidsecond transistor is coupled to said fourth signal, and wherein saidthird signal and said fourth signal providing the output for thevariable phase shifting circuit and are produced by shifting phases ofsaid first signal and said second signal and degrees of shift of saidphases are varied by varying said current to said first transistor andsaid second transistor.
 2. A variable phase shifting circuit accordingto claim 1, wherein said at least one resistor element comprises: afirst resistor element connected to said first signal, for outputtingsaid third signal; and a second resistor element connected to saidsecond signal, for outputting said fourth signal.
 3. A variable phaseshifting circuit according to claim 2, wherein said second signal issupplied to have a predetermined potential.
 4. A variable phase shiftingcircuit according to claim 1, wherein said at least one resistor elementcomprises: a first resistor element connected to said first signal, foroutputting said third signal, and wherein said second signal isoutputted as said fourth signal.
 5. A variable phase shifting circuitaccording to claim 4, wherein said second signal is supplied to have apredetermined potential.
 6. A variable phase shifting circuit accordingto claim 1, wherein the collector of said first transistor and thecollector of said second transistor are connected to a firstpredetermined potential, the base of said first transistor is connectedto said third signal, and the base of said second transistor isconnected to said fourth signal; and wherein said constant currentsource is connected between the emitters of said first and secondtransistors, and a second predetermined potential, and wherein saidconstant current source selectively varies the current of said first andsecond transistors.
 7. A variable phase shifting circuit according toclaim 6, wherein said constant current source is a variable typeconstant current source.
 8. A variable phase shifting circuitcomprising: a resistance unit including at least one resistor element,for inputting a first signal and a second signal and also for outputtinga third signal and a fourth signal; a variable capacitance unitcomprising a first transistor, a second transistor operatively coupledto said first transistor and a constant current source for inputting acurrent to emitter arms of said first and second transistors, whereinthe collector of said first transistor and the collector of said secondtransistor are connected to a first predetermined potential, the base ofsaid first transistor is connected to said third signal and the base ofsaid second transistor is connected to said fourth signal; and whereinsaid constant current source is connected between the emitters of saidfirst and second transistors, and a second predetermined potential,wherein said constant current source selectively varies the current ofsaid first and second transistors, and wherein said third signal andsaid fourth signal are produced by shifting phases of said first signaland said second signal and degrees of shift of said phases are varied byvarying said current to said first transistor and said secondtransistor, and a differential amplifying unit coupled to said thirdsignal and said fourth signal for eliminating in-phase signal componentscontained in said third signal and said fourth signal.
 9. A variablephase shifting circuit according to claim 8, wherein said differentialamplifying unit comprises: a third transistor and a fourth transistor,wherein a collector of said third transistor is connected via a thirdresistor element to said first predetermined potential, the collector ofsaid fourth transistor is connected via a fourth resistor element tosaid first predetermined potential, the base of said third transistor isconnected to said third signal, the base of the fourth transistor isconnected to said fourth signal; and a fifth transistor, wherein thebase of said fifth transistor is connected to a third predeterminedpotential, the collector of said fifth transistor is connected to theemitter of said third transistor and the emitter of said fourthtransistor, and the emitter of said fifth transistor is connected via afifth resistor element to a fourth predetermined potential.
 10. Avariable phase shifting circuit according to claim 1, wherein thecollector of said first transistor and the collector of said secondtransistor are connected to a first predetermined potential, and whereinsaid constant current source is connected between the emitters of saidfirst and second transistors, and a second predetermined potential, andwherein said constant current source controls the collector currents ofsaid first and second transistors, and wherein said second signal has athird predetermined potential.
 11. A variable phase shifting circuitaccording to claim 10, wherein said constant current source is a fixedtype constant current source.
 12. A variable phase shifting method,comprising: supplying a first signal and a second signal to a variablecapacitance unit comprising a first transistor, a second transistoroperatively coupled to said first transistor and a constant currentsource for sinking a current from the emitter of said first and secondtransistors; wherein said first signal is phase shifted to produce saidthird signal and said second signal is phase shifted to produce saidfourth signal, and wherein the base of said first transistor is coupledto said third signal and the base of said second transistor is coupledto said fourth signal, and shifting the phase of said first signal andthe phase of said second signal by varying the base-to-emittercapacitances of said first transistor and said second transistor andproviding said third and fourth signals as the phase shifted output. 13.A variable phase shifting method according to claim 12, wherein saidshifting comprises: varying said constant current source to control theamount of collector current of said first and second transistors,wherein said amount of said collector current controls the amount ofbase-to-emitter capacitances of said first and second transistors, andwherein said amount of said base-to-emitter capacitances controlsdegrees of phase shift of said first signal and said second signal toproduce said third signal and said fourth signal.
 14. A variable phaseshifting method according to claim 12, wherein said shifting a phase ofsaid first signal is executed in synchronism with said shifting a phaseof said second signal.
 15. A variable phase shifting method according toclaim 12, further comprising: eliminating in-phase signal componentscontained in said phase-shifted first signal and said phase-shiftedsecond signal.
 16. A variable phase shifting circuit comprising: a firstresistor element connected to a first signal, for outputting a secondsignal; a second resistor element connected to a third signal, foroutputting a fourth signal; a first transistor and a second transistor,wherein the collector of said first transistor and the collector of saidsecond transistor are connected to a first predetermined potential, thebase of said first transistor is connected to said second signal, andthe base of said second transistor is connected to said fourth signal;and a constant current source connected between the emitter of saidfirst transistor and the emitter of said second transistor, and a secondpredetermined potential and wherein the second and fourth signals areprovided as the output for the variable phase shifting circuit.
 17. Avariable phase shifting circuit comprising: a first resistor elementconnected to a first signal, for outputting a second signal; a secondresistor element connected to a third signal, for outputting a fourthsignal; a first transistor and a second transistor, wherein thecollector of said first transistor and the collector of said secondtransistor are connected to a first predetermined potential, the base ofsaid first transistor is connected to said second signal, and the baseof said second transistor is connected to said fourth signal; a constantcurrent source connected between the emitter of said first transistorand the emitter of said second transistor, and a second predeterminedpotential; a third transistor and a fourth transistor, wherein thecollector of said third transistor is connected via a third resistorelement to said first predetermined potential, the collector of saidfourth transistor is connected via a fourth resistor element to saidfirst predetermined potential, the base of said third transistor isconnected to said second signal, the base of said fourth transistor isconnected to said fourth signal; and a fifth transistor, wherein thebase of said fifth transistor is connected to a third predeterminedpotential, the collector of said fifth transistor is connected to theemitter of said third transistor and the emitter of said fourthtransistor, and the emitter of said fifth transistor is connected via afifth resistor element to a fourth predetermined potential.
 18. Avariable phase shifting circuit comprising: a first resistor elementconnected to a first signal, for outputting a second signal; a secondresistor element connected to a third signal supplied to have a firstpredetermined potential, for outputting a fourth signal; a firsttransistor and a second transistor, wherein the collector of said firsttransistor and the collector of said second transistor are connected toa second predetermined potential, the base of said first transistor isconnected to said second signal, and the base of said second transistoris connected to said fourth signal; and a constant current sourceconnected between the emitter of said first transistor and the emitterof said second transistor, and said first predetermined potential.
 19. Avariable phase shifting circuit comprising: a first resistor elementconnected to a first signal, for outputting a second signal, a firsttransistor and a second transistor, wherein the collector of said firsttransistor and the collector of said second transistor are connected toa first predetermined potential, the base of said first transistor isconnected to said second signal, and the base of said second transistoris connected to a third signal having a second predetermined potential;and a constant current source connected between the emitter of saidfirst transistor and the emitter of said second transistor, and a thirdpredetermined potential and wherein the second and third signals areprovided as the output for the variable phase shifting circuit.